1. Field of the Invention
The present invention relates generally to the method of making a multi color mid-wavelength infrared (MWIR) sensor, and a method of attaching a close proximity filter to an focal plane array (FPA) and more particularly, to the detector portion of the FPA. The inventive methods and apparatuses provide improved spectral discrimination for existing FPAs.
2. Description of the Prior Art
Mid-wavelength infrared (MWIR) sensors may be used to detect a jet engine exhaust plume of a target aircraft or missile, or to provide information on the exhaust from an oil refinery. The inventive methods and apparatuses provide improved spectral discrimination for existing FPAs. Currently known solutions for providing this type of performance improvement, however, are complex and costly.
There are a number of approaches in improving the efficacy of an MWIR sensor. For example, FPAs can have a combination of polarization filters and spectral filters or spectral filters with micro lenses added singularly or in combination. Polarization discrimination offers the capability to highlight or suppress different materials in a scene or objects at different orientations. A spectral or close proximity filter with a micro lens array can be used to increase the MTF (modulation transfer function) performance or reduce cross-talk between pixels of existing FPAs.
A spectral or close proximity filter extends the capabilities of existing FPA technology beyond conventional amplitude/intensity imaging. Close proximity filters can be designed for spectral discrimination, polarization discrimination, and may be coupled with micro lens arrays for focusing/directing light.
Another approach to improve the performance of MWIR sensors consist of FPA technology using detectors with multiple wavelengths within the same unit cell. While this provides for a broader range of detection capability this approach is costly and has a low production yield due to complex semiconductor growth and processing issues.
Yet another approach employs detectors with different cut-off wavelengths in the same imaging system. This requires an extremely precise optics design, which uses a beam splitter to focus the incoming signal on two separate detectors with sub 10th pixel accuracy.